THE  EFFECT  OF  HIGH  TEMPERATURES  ON  THE 
GERMINATION  AND  SUBSEQUENT 
GROWTH  OF  CORN 


BY 

AARON  RAYMOND  KIENHOLZ 

B.S.  North-Western  College,  1917 
M.S.  University  of  Illinois,  1920 


THESIS 

SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS 
FOR  THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY  IN  BOTANY 
IN  THE  GRADUATE  SCHOOL  OF  THE  UNIVERSITY 
OF  ILLINOIS,  1922 


URBANA,  ILLINOIS 


UNIVERSITY  OF  ILLINOIS 


THE  GRADUATE  SCHOOL 


May 12_, 192.  2 


I HEREBY  RECOMMEND  THAT  THE  THESIS  PREPARED  UNDER  MY 

SUPERVISION  BY _ Aaron  Raymond  KienhoJLz 

ENTITLED The  Ef  f.  eat  of  High  Temperatures  on  the 

_ Germination  and  Sub sequent  Growth  of  Corn 

BE  ACCEPTED  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR 
THE  DEGREE  OF  Doctor  of  Philosophy in  Botany 


Recommendation  concurred  in* 


$ si LO, 


Committee 

on 

Final  Examination* 


•Required  for  doctor’s  degree  but  not  for  master’s 


489049 


Digitized  by  the  Internet  Archive 
in  2016 


https://archive.org/details/effectofhightempOOkien 


TABLE  OF  CONTENTS 


I.  INTRODUCTION 1 

1.  Acknowledgment 5 

II.  MATERIALS 6 

1.  Description  of  corn  used. 

2.  Selection  of  corn. 

III.  METHODS .17 

1.  Apparatus  used. 

2.  Mixtures  to  secure  temperatures. 

3.  Treatment  of  corn  after  heating. 

4.  Methods  used  in  heating. 

IV.  RESULTS  AND  DISCUSSION 27 

1.  Heating  of  air-dry  corn  at  100°,  90° , 80°  and  70°C 27 

2.  Desiccation  over  sulphuric  acid 33 

3.  Moisture  determinations ..43 

4.  Gradient  of  Desiccation 48 

5.  Daily  Variation 52 

6.  Placing  in  water  after  heating 56 

7.  Growth  in  soil,  of  heated  corn 58 

V.  CONCLUSIONS 62 

VI.  LITERATURE  CITED 64 

VII.  VITA 66 


i 


-1- 


I.  INTRODUCTION. 

There  has  been  a considerable  increase  in  the  use  of  heat  in  the 
disinfection  of  cereals  against  both  insect  and  fungous  pests,  with- 
in recent  years.  Several  publications  have  been  issued  with  a view 
to  disseminating  knowledge  among  farmers,  seedsmen  and  millowners, 
for  the  control  of  insects  affecting  stored  grains  and  mill  products. 
These  publications  are  of  value  for  that  purpose,  but  the  investiga- 
tions upon  which  they  are  based  too  often  neglect  phases  of  the  sub- 
ject which  are  of  intense  interest  to  the  plant  physiologist  from  a 
scientific  point  of  view  and  to  the  farmer  and  seedsman  from  a 
practical  point  of  view.  The  investigators  have  too  often  been  en- 
tomologists interested  only  in  the  destruction  of  the  insect  pests, 
or  heating  and  ventilating  engineers,  with  the  same  end  in  view. 

They  have  paid  some  attention  to  the  effect  of  the  heat  upon  the 
edibility  and  keeping  qualities  of  the  grain  but  have  seldom  paid 
the  amount  of  attention,  that  the  subject  deserves,  to  the  effect  of 
sterilizing  measures  on  the  viability  of  the  grain.  They  have  not 
worked  with  carefully  controlled  temperatures  or  periocfc  of  exposure 
and  seldom  give  details  as  to  the  moisture  content  of  the  seed,  the 
method  of  heating  or  the  variety,  or  even  the  kind  of  seed  used. 
Furthermore,  detailed  and  careful  experiments  are  seldom  carried  out 
to  determine  the  percent  of  germination  after  the  treatment. 

This  kind  of  investigation  is  often  useless  to  the  botanist  seek- 
ing for  definite  information,  but  more  important,,  it  is  sometimes 
positively  harmful  to  farmers  and  seedsmen,  who,  acting  on  the  in- 
formation given,  treat  their  seed,  only  to  find  the  germination 
lowered  or  the  seed  killed  outright.  Goodwin  (1922)  makes  this 


< 


. 

, 

. 

. 

( < 


-2- 

statement  in  an  Ohio  Experiment  Station  publication,  "Corn  heated  to 
a temperature  of  140°F  (60°C)  for  almost  2 days  germinated  almost  as 

well  as  an  untreated  sample  from  the  same  lot”.  But  adds,  “Of  course 
there  is  the  possibility  that  damp  seed  might  be  injured  by  being 
raised  too  rapidly  to  such  temperatures  as  here  recorded”.  Although 
I did  not  heat  corn  at  60°C , I did,  however,  get  severe  injury  after 
heating  corn  at  70°C  for  140  minutes,  germination  being  reduced  from 
about  98  percent  to  40  percent.  The  corn  I used  contained  about  10.5 
percent  moisture,  which  is  lower  than  the  moisture  content  of  most 
air-dry  corn.  Similarly,  de  Ong  (1919)  working  with  various  seeds, 
including  corn,  gives  heat  treatments  of  100°-  158°F  for  5 hours, 
124°-154°F  for  2 hours,  and  125 °F  for  8 hours  and  gets  an  average 
germination  percent  of  86  percent,  88  percent  and  94  percent  respect- 
ively. He  says  the  effect  on  grains  is  so  small  as  to  be  almost 
negligible.  Corn  is  included  among  the  grains,  though  it  is  much 
more  sensitive  to  heat  than  wheat  and  barley, and  would  be  injured  by 
heat  which  would  not  affect  these  grains. 

The  artificial  drying  of  cereals  or  other  seeds  to  prevent  loss 
in  storage  should  likewise  be  carried  on  under  carefully  controlled 
conditions  and  at  temperatures  known  to  be  low  enough  not  to  injure 
the  viability  of  the  corn  at  a given  moisture  content.  This  is  es- 
pecially important  in  the  drying  of  corn  to  be  used  for  seed,  during 
seasons  when  frost  necessitates  an  early  harvesting  of  the  crop, 
while  it  is  full  of  moisture  and  liable  to  “heat"  in  storage,  unless 
dried.  Insufficient  data  is  available  on  the  moisture-temperature 
relations  of  most  of  our  cereal  seeds  and  one  of  the  purposes  of 
this  investigation  was  to  determine  the  temperature  relations  of 
air-dry  ahd  desiccated  corn. 


, ■ . 


With  the  failure  to  control  certain  seed  borne  diseases  by  means 


of  chemical  disinfectants,  lias  come  the  attempt  to  control  them,  first 
by  hot  water  treatments,  then  dry  heat  treatments,  and  finally  heat 
following  soaking  treatments.  Here  again  we  find  insufficient  atten- 
tion paid  to  the  effect  of  these  treatments  on  the  germination,  and 
above  all,  on  the  subsequent  growth  and  yield  of  the  plants  from 
treated  seed.  Many  seed  borne  diseases,  especially  those  where  the 
fungus  is  within  the  seed  itself,  are  being  studied  and  an  attempt 
made  to  control  them  by  dry  heat.  Atanasoff  and  Johnson  (1920)  have 
reviewed  the  earlier  work  on  the  use  of  dry  heat  in  the  control  of 
disease,  preparatory  to  a discussion  of  their  own  results  on  the  con- 
trol of  various  cereal  diseases  borne  on  the  seeds  of  wheat,  barley, 
rye  and  oats.  They  heated  these  seeds  in  a gas  or  electric  oven  at 
100°C  for  15  and  30  hours*  They  state  that  the  germination,  in  sand, 
was  lowered  slightly  compared  with  untreated  checks,  and  that  the 
plants  from  treated  seed  were  slow  to  start  but  soon  caught  up  with 
their  checks  and  remained  normal.  They  make  no  mention  of  the  kind 
of  container  in  which  the  seed  was  heated,  whether  the  seed  was 
spread  out  in  a thin  layer  or  heaped  together  in  a smaller  container, 
nor  do  they  mention  moisture  content  beyond  saying,  ’’good  dry  seed 
of  barley,  wheat,  oats  and  rye  is  able  to  withstand  suprisingly  well 
the  high  temperature  used,  up  to  30  hours "y  These  results  should  by 
no  means  be  interpreted  as  being  applicable  to  corn  and  before  this 
method  of  seed  treatment  is  broad  casted  among  farmers  or  seedsmen, 

additional  work  should  be  done,  to  determine  what  is  meant  by  "good 
dry  seed"  and  how  frequently  it  exists  in  the  farmer’s  bins  under 

ordinary  storage  conditions*  Dickson  (1920)  working  at  the  same 

station  as  Atanasoff  and  Johnson  (1920)  later  recommends  3 hours 


-4- 

exposure  to  100°C  as  a control  measure  against  wheat  scab  and  seed- 
ling blight  of  wheat,  but  says  nothing  further  concerning  methods. 
Walker  (1922)  has  attempted  to  control  cabbage-black  leg  by  means  of 
dry  heat  treatment  of  the  seed.  He  has  made  moisture  determinations 
of  the  seed  treated. 

With  the  increasing  importance  of  root  and  stalk  rots  of  corn  in 
the  United  States,  comes  the  attempt  to  control  or  lessen  its  damage 
Soil  treatments  have  proved  unreliable,  and  seed  treatments  have 
proved  unsatisfactory,  although  Branstetter  (1922)  reports  a lessen- 
ing in  the  number  of  diseased  plants  from  seed  treated  by  immersion 
in  alcohol  and  mercuric  chloride,  as  compared  with  untreated  checks. 
The  possibility  of  heat  treatment  presents  itself,  but  before  this 
is  attempted  we  should  know  something  of  the  temperature  relations 
of  the  corn  to  be  treated. 

To  determine  the  time -temperature  relations  of  corn  with  known 
amounts  of  moisture,  especially  in  the  air-dry  condition;  to  deter- 
mine the  effect  of  desiccation  on  viability  and  resistance  to  heat, 
and  to  note  the  effect  of  heat  treatment  of  the  seed  on  the  subse- 
quent growth  of  the  seedling,  are  the  facts  to  be  established  in 
this  investigation. 

Three  types  of  corn,  varying  in  amount  of  infection  and  suscepti- 
bility to  disease  under  field  conditions,  and  varying  in  physical 
composition, were  used  in  determining  the  above  facts,  and  any  varia- 
tion in  response  to  the  conditions  imposed  by  the  experiment,  was 
noted,  in  the  hope  of  being  able  to  explain  this  variation  by  means 
of  the  characteristics  of  the  different  kinds  of  corn  used.  Thus  de- 
termining the  characters  wrhich  govern  the  behavior  of  corn  in  re- 
sponse to  various  factors,  such  as  temperature  and  humidity. 


g 

. 

. 

. 

. 


, 

. 


' 


. 


, 


ACKNOWLEDGMENT 


The  work  upon  which  this  thesis  is  based  was  done  in  the 
Laboratory  of  Plant  Physiology  under  the  direction  of  Prof. 
Chas . E.  Hottes  and  the  writer  gratefully  acknowledges  his 
help  in  the  selection  of  the  problem,  in  its  development, 
and  in  the  presentation  of  the  results. 


. 


-6- 


II.  MATERIALS. 

Three  types  of  corn  were  used  in  this  investigation.  These  three 
types  varied  as  to  their  physical  characters,  vitality  and  degree  of 
infection  with  various  root-rot  fungi.  All  three  types  were  of  the 
Reid's  Yellow  Dent  variety,  were  from  the  1920  harvest  and  were  fur- 
nished by  Mr.  J.  R.  Ho  lb  ert,  plant  pathologist  in  the  U.  S.  Depart- 
ment of  Agriculture, of  Bloomington,  111.  According  to  results  ob- 
tained on  the  germinator,  Mr.  Holbert  classified  them  as:  (1)  Ap- 
parently diseased;  (2)  Original  composite  (badly  diseased)  and,  (3) 
Apparently  disease-free.  Throughout  this  investigation  these  types 
of  corn  will  be  known  as:  (l)  Peoria  County  Bad  (PCB)  , (2)  Pox  (Fox) 
and,  (3)  Peoria  County  Good  (PCG)  respectively.  Each  of  these  three 
types  he  further  classified  according  to;  (1)  physical  characters, 
(2)  vitality,  and,  (3)  degree  of  infection. 

The  physical  characters  of  these  types  of  corn  are  of  interest 
because  of  the  correlation  known  to  exist  between  them  and  resist- 
ance or  susceptibility  to  root-rots. 

They  are  classified  as;  (l)  physical  composition  of  kernels,  (2) 
indentation  of  kernels,  (3)  brightness  of  shanks,  (4)  brightness 
of  kernels,  (5)  development  of  kernels,  (6)  tip  covering  of  ears 
and  (7)  lustre  of  ears.  Of  these;  physical  composition,  indentation, 
brightness  and  development  of  the  kernels,  come  under  direct  consid- 
eration in  this  investigation.  These  characters,  expressed  in  per- 
centages are  summarized  in  Table  I. 


• 

t 

: 

. 

< 

: - 

, 

t 

. 

. 

, 


« « 

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, ' : 


. 


Cabla  I.  iPhysical  Characters  of  Gom 


Figure  3.  Rough  ears  of  Fox. 


-10- 


-11- 


Figure  4.  Smooth,  medium  and  rough  ears 
of  PCG , PCB  and  Fox. 


-12- 


From  this  table  it  is  noted  that  PCG  corn  possesses,  to  a high  de- 
gree, many  of  the  physical  characters  which  are  correlated  with 
slightly  infected,  resistant  corn.  Thus;  it  has  a high  percent  of 
horny,  smooth,  bright,  plump  kernels;  good  lustre  of  ears,  and  ears 
with  tips  covered.  PCB  corn  has  a few  of  the  characters  correlated 
with  infected,  susceptible  corn,  such  as;  dull,  shriveled  kernels 
and  dull  lustre  of  ears.  More  important,  however,  is  its  large  per- 
cent of  starchy  kernels.  My  results  indicate  that  this  character  is 
correlated  with  its  ability  to  take  up  and  give  off  moisture  and 
largely  determines  its  subsequent  behavior.  Pox,  on  the  other  hand, 
has  many  of  the  characters  common  to  badly  diseased  corn,  such  as; 
a high  percent  of  rough,  medium  bright  and  medium  starchy  kernels; 
and  medium  lustre  of  ears.  Its  high  percent  of  medium  starchy  ker- 
nels accounts  for  its  behavior  in  regard  to  moisture  content. 

My  own  observations  on  the  ears  used  in  this  study,  coincide 
with  those  of  Mr.  Holbert,  made  on  the  entire  lot  from  which  the 
ears  which  I used  were  taken. 

Figures  1,  2 and  3 indicate  the  smooth  ears  of  PCG;  the  medium  ears 
of  PCB,  and  the  rough  ears  of  Fox,  while  these  may  be  more  easily 
compared  in  Figure  4. 

After  germinating  30  kernels  from  each  ear,  noting  its  percent 
of  germination,  the  degree  and  kind  of  infection  on  the  germinator, 
Mr.  Holbert  classified  each  of  the  types  according  to  vitality  and 
degree  of  infection. 


-13- 

TABLE  II.  VITALITY  AND  DEGREE  OE  INFECTION. 


Type  of 
corn 

Vitality 

Degree  of  Infection 

Fusarium  Diplodia 

PCB 

99.48 

3.45  

Fox 

96.5 

12.7  1.5 

PCG 

99.4 

0.9  ..... 

It  is  not  to  "be  thought  that  because  the  words  rtBadM  and  "Good" 
are  used  in  designating  two  of  the  types  of  corn,  the  vitality  of 
the  former  is  low.  These  terms  refer  to  relative  susceptibility  to 
disease  under  field  conditions.  Mr.  Holbert’s  tests  show  PCB  to 
have  a slightly  higher  percent  of  germination  than  PCG,  while  my 
tests,  (PCB-96.8^;  Fox-93. 2%  PCG-97.4^)  on  the  corn  used,  show 
PCB  to  have  a lower  percent  of  germination  than  PCG.  My  tests  show 
a lower  percent  throughout,  probably  due  to  greater  age  of  the  corn 
and  less  ideal  growth  conditions  obtaining  in  the  rag  doll. 

Tables  I and  II  were  constructed  from  unpublished  data  kindly 
furnished  by  Mr.  Holbert,  to  whom  thanks  are  due. 

The  corn  was  received  at  the  laboratory  on  the  ear  and  was 
stored  in  a dry  place  in  large  covered  tin  boxes.  In  the  early 
work  individual  ears  of  each  type  were  used  as  the  source  of  the 
corn  tested,  record  being  kept  of  the  number  of  the  ear,  and  all 
of  the  good  kernels  from  the  ear,  except  those  at  the  extreme  tip 
and  butt,  being  used.  It  was  soon  noticed  that  individual  ears 
varied  widely  in  their  resistance  to  heat,  their  vigor  of  germina- 
tion and  their  degree  of  infection.  In  order  to  arrive  at  the  ex- 
tent of  this  variation, 6 ears  of  each  type  were  taken  at  random 
and  were  tested  at  80°  and  90°C.  The  results  of  these  tests  are 


summarized  in  Table  III 


-14- 


Tabla  III,  — Individual  Variation  of  the  Ears — Stannary. 


Peoria  Gounty  Bad, 

Fox 

Peoria  County  G-ood 

o 

u . 

o 

© u 

First 

trial 

2nd 

trial 

■Cl© 

I 

CD 

O 

o 

90u  Aver- 
age 

© Ih 

•§a 

I 

30° 

90° 

Aver- 

age 

g* 

CO 

o 

o 

90  J 

80° 

90° 

Aver- 

age 

70 

t.  r r 
OU»  u 

50.0 

58.3 

12 

57.5 

32.0 

44.8 

17 

30.0 

50.0 

16.7 

40.0 

34.2 

72 

86.7 

47.5 

67.1 

28 

62.5 

12.0 

37.3 

18 

40.0 

50.0 

20.0 

33.3 

35.8 

116 

80.0 

50.0 

65.0 

37 

62.5 

36.0 

49.3 

33 

57.5 

57 1 5 

43.3 

40.0 

49.6 

lb  7 

86.7 

47.5 

67.1 

38 

55.0 

36.0 

45.5 

54 

37.5 

57.5 

23 . 5 

45.3 

40.4 

166 

91.7 

50.0 

70.9 

55 

55. 0 

40.0 

47.5 

80 

55.0 

52.5 

43.3 

43.3 

43.5 

176 

76.6 

SO.  Q 

68.3 

75 

67.5 

40.0 

53.8 

93 

55.  Q 

37.5 

20.0 

30,0 

50.5 

70 

,58.*  8 

78.3 

88.6 

12 

38.4 

93.0 

65.7 

17 

61.3 

65.8 

9.7 

74.3 

52.8 

72 

96.0 

86.5 

91.3 

28 

MiA 

78.3 

62.6 

18 

46.5 

68.3 

5.7 

85.7 

51.6 

116 

90.5  122.0 

110.3 

37 

30.6 

121.3 

76.0 

33 

51.5 

34.5 

21.7 

61.3 

54.8 

lb? 

88.5 

66.0 

77.3 

38 

37.4 

92.8 

65.1 

54 

30.5 

41.0 

22.7 

40.3 

38.6 

166 

89.0 

65.3 

77.2 

55 

37.0 

89.8 

63.4 

80 

73.3 

72.0 

11.3 

99.7 

64. 1 

176 

85.2 

77.3 

81.3 

75 

40.8 

79.8 

60.3 

93 

37.8 

62.5 

5.7 

70.3 

44.1 

© 

c5 

o 


© 


► 


-15- 


Some  ears  did  not  vary  widely  from  the  average,  or  were  not  con- 
sistent in  their  variation,  while  others;  notably,  Fox  #75  and  PCG 
#33  were  consistently  high  in  percent  of  germination  and  length  of 
plumule,  and  still  others;  as  PCG  #93  were  lew  in  percent  of  germina- 
tion and  length  of  plumule. 

The  corn  kernels  often  had  their  coats  broken,  especially  was  this 
true  of  the  rougher  ears  such  as  those  of  Fox,  where  the  shriveled, 
attenuated  crown,  which  caused  the  roughness  of  the  ears,  is  very 
easily  broken.  These  kernels  were  discarded,  as  were  also  those  in- 
jured by  the  grain  moth.  Some  kernels  had  their  tips  broken  off, 
exposing  the  black  cap  covering  the  lower  part  of  the  embryo.  To  de- 
termine whether  these  kernels  were  more  readily  injured  by  heat  than 
those  with  the  tips  intact  tests  were  made,  using  the  three  types  of 
corn.  The  tips  were  in  most  cases,  broken  off  artificially,  but 
differed  ih  no  way  from  those  whose  tips  were  broken  off  in  the  shell- 
ing process. 

Kernels  with  tips  broken  off  gave  39.3  percent  germination, while 
kernels  with  tips  intact  gave  44.7  percent  germination,  a difference 
of  5.4  percent.  There  was  practically  no  difference  in  length  of 
plumule.  Each  type  responded  similarly  to  this  treatment.  No  tests 
were  made  of  kernels  with  their  crowns  broken,  though  results  would 
probably  have  been  less  significant  than  those  given  above.  This 
difference  justified  me  in  selecting  onl}'-  kernels  with  tips  intact. 

Because  of  the  variation  between  individual  ears,  most  of  the  in- 
vestigation was  carried  on  with  composite  samples  obtained  by  select- 
ing the  same  number  of  good  kernels  from  each  ear  and  mixing  them 
thoroughly.  This  composite  was  kept  in  tin  cans  in  the  laboratory. 

By  selecting  50  kernels  from  each  ear,  and  having  63  ears  of  PCB , 

33  ears  of  Fox,  and  45  ears  of  PCG  to  select  from,  enough  corn  of 


, 


< 

. 

. 

, 


, 


, 

. 

. 


. 


. 

< , 


-16- 

a fairly  composite  nature  was  obtained  for  a period  of  work,  and  this 
was  repeated  as  more  corn  was  needed. 

These  investigations  involve  the  use  of  30,000  kernels,  tested  in 
lots  of  10  and  25,  unless  otherwise  indicated. 


. 


„ 


-17- 


III.  METHODS . 

The  apparatus  used  in  the  heating  of  the  seeds  was  similar  to  that 
used  by  Groves  and  described  by  him  in  the  Transactions  of  the  111. 
Academy  of  Science  8:133-136,  1915,  It  consisted  of  two  copper 
baths  15.5  cm.  high,  21  cm.  in  diameter  with  a capacity  of  about  4 
liters.  (Fig . 5)  The  top  was  perforated  by  10  tubulatures,  3 cm. 
in  diameter,  around  the  periphery  and  one  in  the  middle.  These  baths 
were  placed  on  electric  hot  plates.  They  were  exactly  the  size  of 
the  hot  plate  and  a galvanized  iron  sleeve  was  fitted  around  the  base 
of  the  bath,  extending  down  over  the  hot  plate  thus  preventing  rapid 
radiation  of  heat  and  at  the  same  time  holding  the  bath  in  place.  In 
the  center  tubulature  of  each  boiler  a double  bulb  reflux  condenser 
made  of  block  tin  was  tightly  fitted.  The  temperature  of  the  bath 
was  measured  by  a standard,  go vernment- tested , Centigrade  thermometer 
which  could  be  slipped  in  and  out  of  a glass  tube  leading  down  into 
one  of the  glass  phials  described  below.  One  of  these  thermometers 
was  fitted  into  a tubulature  in  each  boiler.  These  phials  contained 
corn  to  keep  the  bulb  of  the  thermometer  from  having  direct  contact 
with  the  glass.  This  left  9 tubulatures  which  could  be  used  for  the 
heating  of  the  corn. 

The  glass  phials  were  9 cm.  x 2 cm.  and  were  fitted  with  rubber 
stoppers  thru  which  extended  6 inch  capillary  tubes  of  1 ram.  bore. 
These  capillary  tubes  were  used  to  allow  for  the  escape  of  the  ex- 
panding , heating  air  and  thus  hasten  a rapid  adjustment  of  tempera- 
ture. Several  tests  were  made  to  determine  whether  a difference  in 
the  size  of  the  opening  leading  down  into  the  phial  resulted  in  a 
difference  in  the  percent  of  germination.  A series,  using  the  cap- 
illary glass  tubes,  with  openings  1 mm.  in  diameter,  was  contrasted 

with  one  using  the  ordinary  glass  tubes  with  openings  4 mm.  in 

- — — — 


♦ 

t 

• 

■ 

t 

< 

• 

* 

< 

• 

< 

. 

. 

. 


< 

- 


. 

( 


-18- 


Figure  5.  Apparatus  used  in  heating. 


diameter.  The  average  percents  of  germination  of  three  trials  at 
80°  and  90°C  were  10.6  percent  and  .3  percent  in  favor  of  the  ordina- 
ry glass  tubes  and  4.0  percent  in  favor  of  the  capillary  tubes.  The 
plumule  lengths  vary  slightly  in  the  same  way.  These  results  would 
indicate  that  this  slight  difference  in  size  of  openings  has  little, 
if  any,  effect  on  the  resistance  of  the  treated  corn  to  heat,  A 
larger  rubber  stopper  at  the  upper  end  of  the  capillary  tube,  fitted 
the  tubulatures  in  the  copper  bath  and  supported  the  phial  in  the 
liquid.  (Fig.  5)  By  adjusting  the  distance  between  the  two  stoppers, 
the  phials  were,  in  all  cases,  completely  submerged,  in  order  to 
make  the  temperature  of  the  phials  uniform  throughout  and  also  to 
make  visible  any  leakage  which  might  occur  around  the  stoppers.  If' 
any  leakage  did  occur  the  test  v/as  of  course  discarded.  When  not  in 
use  the  tubulatures  in  the  boiler  v/ere  kept  tightly  closed  with  corks 
in  order  to  reduce  to  a minimum  the  loss  from  evaporation  and  the  con1 
sequent  change  in  the  boiling  point  of  the  fluid. 

To  obtain  the  temperatures  desired,  advantage  was  taken  of  the  dif- 
ferent boiling  points  of  various  liquids  and  various  mixtures.  Thus; 
to  secure  a temperature  of  100°  a mixture  of  glycerine  and  water  was 
used  in  the  proportion  of  13$  glycerine  to  87$  water.  This  mixture 
boiled  at  exactly  100°C  and  the  condenser  refluxed  the  liquid  back 
into  the  boiler,  thus  maintaining  a uniform  temperature.  To  secure  j 
temperatures  of  90°C  and  80°C,  mixtures  of  ethyl  alcohol  and  water 
were  used,  while  to  secure  a temperature  of  70°C  a mixture  of  methyl 
alcohol  and  water  was  used.  The  exact  proportions  of  the  mixtures 
used  are  summarized  below: 


■ 


" , 

, 

. 

. 


. 


* 


. 


, 


• 

* 

-20- 

Temperature  Distilled  Water 


100°  c 

87  $ 

- g lycerine  - 13$ 

90°C 

75$ 

- ethyl  alcohol  - 25$ 

80°C 

58% 

ethyl  alcohol  - 62$ 

70°C 

15% 

- methyl  alcohol  - 85$ 

Distilled  water  was  used  in  each  case  and  ordinary  commercial 
alcohols  and  glycerine.  The  high  temperature  and  the  vapor  from 
the  boiling  liquids  quickly  deteriorated  the  corks  and  some  evapora- 
tion occured,but  the  temperatures  were  carefully  adjusted  before 
each  trial.  If  care  was  taken  not  to  add  too  many  phials,  at  a time, 
the  temperature  variation  could  easily  be  kept  within  ,5°C. 

The  phials  were  kept  dry  and  clean  inside  and  were  warmed  before 
loading,  to  hasten  the  change  in  temperature  to  that  of  the  bath. 
With  the  high  temperatures  and  short  periods  of  heating  this  became 
an  important  factor.  This  makes  it  difficult  to  determine  what  the 
actual  heat  experienced  by  the  embryo,  was.  This  difficulty,  how- 
ever, has  been  experienced  by  every  investigator  of  temperature  in 
its  effect  on  seeds.  The  conditions  were  uniform  for  each  type  of 
corn  and  should  introduce  no  error  here.  In  an  effort  to  determine 
the  speed  of  this  temperature  rise,  phials  fitted  with  thermometers 
were  inserted  in  the  bath  and  the  time  required  to  reach  certain 
temperatures  was  noted.  At  first  the  temperature  rise  was  very  rap- 
id, but  gradually  slowed  up  until  it  was  difficult  to  determine  its 
rate  of  rise,  so  slowly  did  it  change.  An  average  of  about  15  min- 
utes was  required  for  empty  phials  to  change  from  28°C  to  99.50(3. 
Starting  at  28°C  - 40OC  was  reached  in  24  sec. 

90°C  was  reached  in  4 min. 

99.5°C  was  reached  in  14  min.  30  sec. 


, 


< 


, 


• 

• , 

. 

, 

* 

- 

. 

. 


, 


-21- 


When  the  phials  were  loaded  the  rise  in  temperature  was  even  slower 
than  in  the  case  of  empty  phials.  With  a load  of  25  kernels,  97.5°C 

was  the  average  temperature  reached  at  the  end  of  15  minutes. 

After  the  corn  had  been  heated  the  phials  were  removed  from  the 
bath  and  the  corn  immediately  placed  in  small  aluminum  dishes  to 
cool.  The  corn  was  then  placed  in  rag  dolls  to  germinate. 

The  rag  dolls  used  were  of  two  kinds;  one  made  from  a strip  of  un- 
bleached muslin,  12x56  inches  and  marked  into  6 spaces  6x4  inches, 
each  space  to  accomodate  10  kernels.  This  kind  was  used  very  little 
The  kind  most  used  was  made  of  a good  grade  of  bleached  muslin,  8|- 
x48  inches,  issued  by  the  State  Council  of  Defense,  during  war  time. 
Six  lots  of  10  seeds  each  were  placed  in  one  rag  doll  thus  giving 
ample  room  for  germination  and  growth. 

The  dolls  were  thoroughly  washed,  scrubbed  and  boiled,  before 
using,  insuring  a certain  amount  cf  freedom  from  saprophytic  fungi. 
The  modified  rag  doll  as  described  by  Duddleston  (1920)  was  used  onty 
where  the  relative  degree  of  infection  was  sought  for.  The  ordinary 
unwrapped  method  proved  adequate  to  show  germination  vigor  and  was 
much  quicker  and  cheaper  than  the  modified  method.  The  dolls  were 
placed  in  luke-warm  tap  water  and  allowed  to  soak  for  10  hours.  They 
were  then  removed  and  allowed  to  drain  thoroughly  and  placed  in 
gallon  jars  provided  w'ith  drainage,  and  other  jars  placed  over  them. 
(Fig.  6)  This  arrangement  proved  satisfactory  and  convenient.  These 
germinators  were  placed  in  a temperature  case  with  the  temperature 
accurately  regulated  at  30°C.  Haber landt  (1874)  gives  the  optimum 
temperature  for  the  germination  of  corn  as  34.0°C  and  Lehenbauer 
(1914)  says  the  optimum  temperature  for  the  growth  of  maize  seedlings 
is  between  29°  and  32°C.  But  the  advantages  of  the  constant  temper- 
ature and  the  fact  that  the  temperature  case  was  a permanent  part  of 


/ 

Figure  6.  Germinator  jars. 


Figure  7.  Hag  dolls,  showing  wire  cores, 
and  a Daily  Variation  test,  ready  to  read. 


-23- 


the  laboratory’s  equipment  outweighed  the  disadvantage  of  building 
apparatus  to  make  possible  a slight  raise  in  temperature  to  the  op- 
timum. After  5 days  (including  the  soaking  period),  at  30°C , the  rag 
dolls  were  opened  and  read  for  amount  of  germination  and  length  of 
plumule,  (Fig.  7) 

It  is  realized  that  the  rag  doll  is  not  an  ideal  method  of  germi- 
nating corn,  but  it  is  the  quickest,  best  method  of  handling  a large 
number  of  germinating  kernels  in  a way  that  would  make  the  results 
comparable  to  those  obtained  by  the  farmer  in  testing  his  corn.  Every 
method  has  its  disadvantages  but  those  of  the  rag  doll  seemed  least, 
it  being  readily  available,  compact,  quickly  and  easily  handled,  and 
tends  to  familiarize  one  with  a method  much  used  throughout  the 
country.  It  was  noticed  that  the  outside  of  the  rag  doll  gave  slight 
ly  poorer  germination  than  the  inside  and  that  the  lower  part  of  the 
rag  doll  gave  poorer  germination  than  the  upper  part. 

The  wire  cores,  (Eig.  7)  on  which  the  rag  dolls  were  rolled  prob- 
ably gave  as  great  aeration  to  the  inside  of  the  dolls  as  the  outside . 
This,  coupled  with  better  moisture  conditions  gave  better  germina- 
tion on  the  inside  than  the  outside..  Too  much  moisture  caused  a 
lower  germination  in  the  lower  part  of  the  rag  doll  than  in  the  upper 
part.  These  variations,  however,  acted  equally  upon  all  three  types 
and  did  not  introduce  an  error  in  the  results. 

Waggoner  (1917)  has  shown  clearly,  one  of  the  reasons  for  the  dis- 
crepencies  in  the  results  obtained  by  earlier  investigators  on  the 
effect  of  high  temperatures  on  seeds,  namely;  the  method  used  in 
heating.  In  his  own  work  he  has  shown  the  decided  difference  in  the 
effect  of  heat  on  viability  when  the  seeds  were  heated  in  an  open 
oven  or  in  flasks.  In  order  to  determine  whether  this  difference 
held  also  for  the  types  of  corn  under  investigation,  air— dry  corn 


. 

« 

. 

. 

. 


. 


, 

. 


, 

. 


* 

< - 


-24- 

was  heated  at  70°C  for  100,  120,  140  and  160  minutes  in  phials  as  al- 
ready described  and  also  in  large  test  tubes,  26  mm.  in  diameter  and 
150  mm.  long.  These  test  tubes  we re  given  several  turns  of  electri- 
cians friction  tape  around  the  top  so  as  to  make  them  fit  the  openings 
in  the  boiler  tightly  and  more  tape  was  used  to  seal  the  tube  in  so 
as  to  prevent  the  escape  of  steam  from  the  bath.  These  test  tubes 
quickly  reached  same  temperature  as  the  bath  and  the  corn  to  be  treat- 
ed was  placed  in  small  wire  baskets  and  lowered  into  these  tubes. 

The  corn  was  thus  in  a dry  heat  equal  to  the  heat  applied  to  the 
phials  and  was  treated  the  same  length  of  time  in  each  case.  In  the 
one  case  there  was  much  space  for  the  moisture  to  escape  from  the 
kernels  while  in  the  case  of  the  phials  fitted  with  capillary  tubes 
a very  limited  amount  of  moisture  could  escape. 

Table  IV  gives  the  significant  results  of  a test  conducted  with  air 
dry  corn  at  70°C 


Table  IV.  Open  test  tubes  compared  with  phials, 
at  70°  C.  with  air- dry  corn. 


Type 

Percent 

of  Germination 

of 

Corn 

100 

Min . 

120 

Min . 

140 

Min . 

160 

Min . 

Average 

T * 

P 

T 

P 

T 

P 

T 

P 

T 

P 

PCB 

SO 

80 

100 

30 

SO 

70 

100 

30 

95  .0 

52.5 

FOX 

100 

40 

80 

50 

60 

20 

60 

13 

75  .0 

30  .5 

PCG 

100 

70 

100 

50 

100 

10 

100 

20 

100  .0 

37  .5 

Average 

90  .0 

40  .2 

*T — refers  to 

the  o 

pen 

test  tubes . 

P— r 

efers  to 

the  p 

hials  . 

Type 

Leng 

th  of 

Plumule 

of 

Corn 

100 

Min . 

120 

Min . 

140 

Min . 

160 

Min . 

. Average 

T 

P 

T 

P 

T 

P 

T 

P 

T 

T> 

X 

PCB 

113 

48 

100 

51 

80 

19 

91 

7 

96.0 

31 .5 

FOX 

71 

7 

76 

15 

29 

10 

42 

8 

54  .5 

10  .0 

PCG 

118 

49 

98 

13 

81 

13 

91 

13 

97.0 

21 .8 

Average 

82.5 

20.8 

-25- 


Waggoner  (1917)  states  that  the  chief  factor  determining  the  re- 
sistance of  seeds  heated  to  the  same  temperature  by  different  methods 
is  the  amount  of  moisture  absorbed  or  lost  during  the  treatment.  On 
this  basis  the  results  given  above  are  undoubtedly  more  significant 
than  they  would  be  at  a higher  temperature,  because  the  long  heating 
period  allows  much  moisture  to  escape  before  injury  or  killing  takes 
place.  At  high  temperatures  and  short  heating  periods  it  is  doubt- 
ful if  any  such  difference  would  be  noted.  The  average  difference  of 
49.8  percent  in  germination  and  61.7  mm.  in  length  of  plumule,  and 
the  consistently  lower  percent  of  germination  and  length  of  plumule 
of  those  kernels  heated  in  phials,  at  all  temperatures  used,  show  con- 
clusively the  difference  due  to  method  of  heating. 

The  corn  after  it  was  heated  was  immediately  placed  in  aluminum 
dishes  to  cool.  Sometimes  it  was  more  convenient  to  allow  the  corn 
to  cool  in  the  phials  in  which  it  was  heated.  This  was  not  done,  on 
the  theory,  that  the  after  effects  of  the  heating  would  continue  much 
longer  if  the  corn  remained  in  the  phials  than  if  it  was  placed  in 
the  dishes  to  cool.  To  test  this  point,  air  dry  corn  was  heated  to 
90°C  for  4-7  minutes,  one  series  being  allowed  to  remain  in  the  cork- 
ed phials  to  cool,  and  the  other  being  placed  in  the  aluminum  dishes 
to  cool.  The  percent  of  germination  of  those  cooled  in  the  phials 
was  60.8  percent  while  the  percent  of  germination  of  those  cooled 
in  the  dishes  was  65.0  percent,  a difference  of  4.2  percent.  Simi- 
larly the  difference  in  plumule  lengths  was  23*3  mm.  in  favor  of 
those  cooled  in  the  aluminum  dishes. 

To  avoid  the  necessity  of  raising  the  temperature  of  the  entire 
phials,  its  contents,  the  stopper  and  capillary  tube  to  the  temper- 
ature of  the  bath,  it  was  thought  desirable  to  construct  an  appara- 
tus which  would  allow  the  temperature  of  the  phial  to  be  raised  to 


. 

« • • •„  f 


. 


. 

, 

. 


. . 

« 

#:  i 

. 

, 

* 

. 


, '■  J 


-26- 

the  temperature  of  the  bath  before  being  loaded.  This  was  done  by 
replacing  the  capillary  tube  by  a large  glass  tube  of  12  mm.  inside 
diameter.  The  phial  was  then  placed  in  position  and  allowed  to  come 
to  the  temperature  of  the  bath.  The  10  kernels  to  be  treated  were 
placed  in  a glass  tube  of  the  same  size  as  that  used  in  the  phial 
and  in  loading , the  kernels  were  allowed  to  slide  from  the  glass 
tube,  down  into  the  phial.  This  was  done  very  quickly  and  the  tube 
leading  into  the  phial  was  then  closed  with  a capillary  tube  to  make 
conditions  comparable  with  the  ordinary  method  of  heating. 

A similar  glass  tube,  enlarged  to  a funnel  form  at  the  top,  was 
passed  thru  an  opening  in  the  top  of  the  electric  oven  and  aluminum 
dishes  were  loaded  without  opening  the  oven  door,  thus  avoiding  a 
drop  in  temperature.  There  seemed  to  be  no  consistent  difference 
between  the  results  obtained  by  using  this  loading  device  and  the 
ordinary  method  of  placing  the  kernels  in  the  cool  phial  and  then 
placing  in  the  bath,  hence  it  was  not  used  except  in  a very  few 
cases. 


-27- 


IV .RESULTS  AND  DISCUSSION. 

EFFECT  OF  HEAT  ON  AIR-DRY  CORN. 

No  extensive  work  has  been  done  on  the  time  and  temperature  re- 
quired to  injure  or  to  kill  corn  by  subjecting  the  kernels  to  heat. 
Almost  without  exception,  where  any  time  and  temperature  are  given, 
no  mention  is  made  of  the  moisture  content  of  the  corn,  though  it  has 
been  known  for  many  years  that  the  drier  seeds  are  the  greater  degree 
of  heat  they  can  withstand.  Miss  White  (1909)  in  her  studies  on  fer- 
ments in  seeds,  heated  corn  at  99-100°C  for  6j?  hours  and  got  no  ger- 
mination, while  corn  heated  for  one  hour  to  122°  and  124°C  was  killed 
Burgess  (1919),  in  investigating  possible  injury  done  to  the  vitality 
of  seeds  by  heat  treatment  for  insect  pests,  found  that  corn  gave  68 
percent  germination  when  treated  at  176°F  (S0°C)  for  1 hour,  and  32 
percent  when  treated  for  3 hours.  Montgomery  (1917),  investigating 
a similar  problem  said,  “the  germinating  quality  of  grain  is  destroy- 
ed at  150°F  (65.6°C)  and  probably  injured  at  5°  less,  if  long  ex- 
posed.” Ear  corn  hanging  in  a seed  room  which  was  disinfected  sever- 
al times  at  140°F  (60°C)  for  several  hours  at  a time,  was  not  appar- 
ently injured. 

All  of  the  work  which  has  been  done,  and  it  is  small  in  amount, 
is  of  the  same  fragmentary  nature  as  that  reported  above.  Thus  it 
seemed  the  first  task  to  find  out  the  exact  time  and  temperature  re- 
lations of  air-dry  corn,  under  the  conditions  of  the  experiment, 
namely;  dry  heat,  applied  to  corn  in  phials  fitted  with  capillary 
tubes,  the  volume  of  the  phial  being  about  8 times  that  of  the  corn. 

It  should  be  borne  in  mind  that  the  moisture  content  of  air-dry 
corn,  as  kept  in  the  laboratory,  averaged;  PCB-10.93  percent,  Fox- 
10.64  percent,  and  FCG-10 ,41percent . These  percentages  are  based 


< 

. 

, 

- 


. ' 

. 


. • 


. 


< 


-28- 

on  the  air-dry  weight  of  the  seed  and  were  determined  as  discussed 
below.  It  is  for  corn  of  the  above  moisture  content , that  the  time 
and  temperature  figures  given  in  Tables  V, VI, VII,  and  VIII,  a.pply. 
Altho  the  moisture  content  of  the  corn  varied  somewhat,  it  was  lower 
than  if  it  had  been  stored  out  of  doors,  subject  to  varying  climatic 
conditions. 

The  average  of  many  moisture  determinations  made  on  samples  from 
all  over  the  state,  by  the  Division  of  Crop  Production,  College  of 
Agriculture,Univer sity  of  Illihois,  is  as  follows:  for  samples  re- 
ceived and  tested  in  February---15  percent,  March-15  percent,  and 
April-12  percent.  These  figures  should  not  be  lost  sight  of  in  the 
drying  of  corn,  or  in  heat  treatments  for  insect  or  fungous  pests. 
Table  V.  Air-Dry  Corn  - 100°C  - Dry  Oven. 


Types  of 
Corn 

Percent  of 

Germination 

Min. 

7£ 

Min. 

10 

Min. 

12£ 

Min. 

15 

Min. 

Average 

PCB  184* 

100 

24 

44 

0 

0 

53.6 

Fox  71 

88 

56 

0 

8 

0 

50.4 

PCG  77 

92 

72 

52 

4 

0 

40.0 

Types  of 
Corn 

Length  of 

Plumule 

( in  mm. ) 

5 

Min. 

7* 

Min . 

10 

Min. 

12£ 

Min. 

15 

Min. 

Average 

j PCB  184 

108 

19 

11 

0 

0 

27.6 

Fox  71 

102 

71 

0 

7 

0 

56.0 

PCG  77 

152 

112 

14 

4 

0 

56.4 

^•-refers  to  number  of  ear  used. 


M ith  vaanii  icmrawg*: 


-29- 

The  corn  heated  at  1C0°C  as  given  in  Table  V,  was  heated  in  the 
electric  oven  in  open  aluminum  dishes.  This  accounts  for  its  not 
being  killed  except  after  15  minutes  exposure,  while  the  same  kind 
of  corn  is  killed  in  9 minutes  at  90°C  when  heated  in  the  phials , 
This  illustrates  again  the  difference  due  to  method  of  heating.  At 
100°C  the  period  required  to  kill,  when  the  phials  were  used,  was  so 
short  that  it  was  difficult  to  get  results  which  were  of  much  value, 
especially  in  view  of  the  slow  rise  in  temperature  in  the  phials,  as 
discussed  under  Methods.  Only  a few  minutes  were  required  to  kill 
when  100°C  was  used,  and  the  actual  temperature  experienced  by  the 
seed  at  the  end  of  this  time  was  undoubtedly  far  below  100°C, 


Table  VI.  Air-Dry  Corn  - 90°C  - Phials. 


Type  of 

Percent 

of  Germination 

Corn 

CHECK 

3 

Min. 

4 

Min. 

5 

Min. 

6 7 

Min.  Min. 

8 

Min. 

9 

Min. 

Average 

PCB 

100 

100 

90 

90 

30  70 

10 

0 

55.7 

Pox 

100 

90 

100 

90 

80  70 

0 

0 

61.4 

PCG 

100 

100 

100 

80 

60  70 

20 

0 

61.4 

Type  of 

Length  of  Plumule  (in 

ram. ) 

Corn 

CHECK 

3 

Min. 

4 

Min. 

5 

Min. 

6 7 

Min. Min. 

8 

Min. 

9 

Min. 

Average 

PCB 

132 

118 

114 

98 

58  103 

5 

0 

70.9 

Pox 

107 

119 

94 

101 

96  52 

0 

0 

66.0 

PCG 

135 

126 

122 

98 

68  89 

51 

0 

79.1 

-31- 


When  90°C  was  used  and  the  corn  treated  in  phials,  complete  kill- 
mg  took  place  at  9 and  10  minutes  while  injury  to  germination  was 

manifest  at  5 minutes.  A slight  decrease  in  plumule  length,  already 
noticeable  at  3 minutes  exposure,  when  compared  to  the  check  may  be 
due  to  retardation  of  germination  and  growth  caused  by  heating, or  it 
may  be  due  to  heat  injury.  It  is  possible  that  the  corn  heated  for 
3 minutes  would  finally  overcome  the  retardation  of  its  growth,  a.nd 
give  as  great  a growth  as  the  check.  No  studies  were  made  on  this 
point,  but  it  is  noticeable  throughout  this  entire  investigation, 
as  it  is  in  Tables  V, VI, VII,  and  VIII,  that  the  length  of  plumule  at 
the  end  of  5 days  is  much  less  from  those  seeds  heated  for  a longer 
period  than  in  those  not  heated  so  long.  Much  of  this  is  due,  I am 
convinced,  to  actual  injury  done  by  the  heat,  which  the  plant  can 

never  overcome.  In  any  case,  the  effects  of  heat  are  more  quickly 
noticeable  in  length  of  plumule  than  in  percent  of  germination* 

Care  must  be  taken,  however,  to  draw  conclusions  only  from  consider- 
able numbers  because  of  the  greater  variation  in  plumule  length, 
than  in  percent  of  germination* 

The  average  of  other  series  run  at  90°C  give  germination  percents! 
of  PCB-68.8,  Pox-60.3,  and  PCG-64.5,  showing  that  PCB  is  not  always 
lowest  in  percent  of  germination,  though  this  is  usually  the  case. 

Air-dry  corn  heated  at  80°C  in  phials,  is  practically  all  killed 
after  20  minutes  and  all  killed  after  25  minutes  exposure.  Injury 
is  already  noticeable  after  10  minutes  exposure. 

A limited  amount  of  work  does  not  allow  me  to  give  the  exact 
length  of  time  required  to  kill  at  70°G,  though  injury  is  apparent 
after  80  minutes  exposure.  A series  which  was  made  unuseable  by 
being  read  too  early,  indicates  that  after  longer  periods  of  ex- 
posure (160  and  180  minutes)  the  Pox  and  PCG  corn  is  almost 

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-32- 

completely  killed  while  the  PCB  corn  germinates  50  and  30  percent. 
The  whole  series  averages;  PCB-55.0  percent,  Pox-28,3  percent  and 
PCG-26.7  percent,  with  the  plumule  lengths  in  a similar  ratio.  This 
behavior  is  similar  to  that  experienced  in  the  heating  of  desiccated 
corn,  discussed  below.  It  further  resembles  the  results  obtained  on 
heating  desiccated  corn,  in  that  the  differences  in  resistance  are 
most  noticeable  at  lengths  of  exposure  which  are  highly  injurious. 
This  is  borne  out  by  the  results  given  in  Table  VIII  where  the  re- 
sistance to  heat  is  exactly  opposite  to  those  obtained  at  80,  90, 


and  100°C. 

PCB 

Pox 

PCG 

Thus:  70°C 

70,0$ 

6670$ 

54.0$ 

Average :80°C 

of  :90°C 

:100°C 

30 . 9$ 

43.3$ 

48.9$ 

This  may  be  due  to  the  greater  amount  of  water  given  off  during  the 
lohg  heating  process,  by  PCB,  than  by  the  other  two  types  of  corn 
and  its  consequent  greater  resistance  to  heat. 

The  average  of  results  for  80,90  and  100°C  given  above,  justifies 
the  statement  that  air-dry  PCB  corn  contains  the  most  moisture  and 
is  least  resistant  to  heat,  PCG  corn  contains  the  least  moisture  and 
is  most  resistant  to  heat,  while  Pox  is  intermediate  in  both  moistur 


content  and  resistance  to  heat 


< 


- 33” 

DESICCATION. 

From  the  earliest  investigators  down  to  the  present  time,  increas- 
ing importance  has  "been  ascribed  to  the  moisture  content  of  grains  as 
affected  by  high  temperatures.  As  a result,  most  recent  articles, 
with  some  notable  exceptions;  dealing  with  the  effect  of  heat  on  via- 
bility are  careful  to  state  fully  the  conditions  of  the  experiment; 
the  seed  used,  the  method  of  heating  and  the  moisture  content  of  the 
seed.  Waggoner  (1917)  has  summarized  the  earlier  work  on  the  relatior 
of  moisture  content  to  viability  of  seed  heated  to  different  degrees, 
and  his  own  work  is  the  first  detailed,  quantitative  piece  of  work, 
using  one  kind  of  seed.  He  has  shown  that  the  resistance  of  seeds  of 
radish,  exposed  to  high  temperatures,  is  inversely  proportional  to 
their  initial  water  content  at  the  time  of  heating. 

The  purpose  of  this  part  of  the  investigation,  then,  was  to  deter- I 
mine  to  what  extent  this  was  true  of  corn,  to  ascertain  the  actual 
time  and  temperature  relations  of  corn  desiccated  for  various  periods 
of  time  as  compared  with  air-dry  corn  and  to  determine  if  the  three 
types  of  corn  used,  responded  similarly  to  this  treatment. 

Two  quart  mason  fruit  jars  were  fitted  with  rubbers  and  tightly 
fitting  screw  covers.  Hooks  were  soldered  into  the  middle  of  these 
covers,  from  which  hung  paraffined  wire  baskets  filled  with  corn. 

(Fig.  8.)  About  150  c.c.  of  concentrated  sulphuric  acid  (sp.gr.  1.84' 
was  placed  in  the  bottom  of  each  jar  as  the  desiccating  agent.  Each 
of  the  three  types  of  corn  were  thus  lowered  in  water  content  and  at 
intervals  corn  from  these  baskets  was  tested  to  determine  its  re- 
sistance to  heat.  Sets  of  these  jars  were  started  at  intervals  in 
order  to  have  a succession  corn  of  different  moisture  contents  for  a 
series  of  trials.  These  jars  were  placed  in  a 30°G  constant  tempera- 
ture case  and  were  removed  only  while  being  tested.  As  the  length 


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-34- 


Figure  8.-  Desiccator,  with 
corn  in  wire  basket  suspended 
over  sulphuric  acid. 


-35- 


of  time  of  desiccation  increased,  the  temperature  used  was  increased 
and  the  time  of  exposure  lengthened.  The  results  of  trials  at  various 
times  and  temperatures,  after  desiccation  of  1,2,4,6,8,9,10,12,14,15, 
17,20,23,27,31  and  100  days  are  given  in  Table  IX.  The  results  are 
expressed  as  percent  of  germination  and  these  are  averaged  at  the  foo 
of  the  table.  Those  treated  at  80°C  are  grouped  in  the  lower  left 
hand  corner  of  the  table,  those  at  100°C  in  the  upper  right  hand  cor- 
ner and  those  at  90°C  in  the  middle  of  the  table,  each  set  of  results 
being  divided  from  the  others  by  a heavy  zig-zag  line. . Thus  the 
three  types  of  corn  which  had  been  desiccated  for  8 days  were  treated 
at  90°C  for  35,40,45  and  50  minutes  and  also  at  80°C  for  100,110,120 
and  130  minutes,  and  the  percent  of  germination  for  each  given  in  its 
proper  place. 


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-36- 

Difficulty  was  encountered  in  determining  the  proper  time  and  tem- 
perature to  use  in  testing  the  corn.  As  desiccation  steadily  de- 
creased the  moisture  content,  the  time  and  temperature  of  treatment 
had  to  he  increased  in  order  to  he  injurious,  and  thus  give  signifi- 
cant results.  With  the  lower  temperatures  this  change  in  time  was 
rapid,  as  shown  hy  the  similar  results  obtained  after  1 days  desic- 
cation, hy  exposure  to  80°C  for  15  minutes  and  after  4 days  desicca- 
tion at  80° C for  85  minutes.  With  the  higher  temperatures,  however, 
this  change  was  slow,  as  shown  hy  the  very  similar  results  obtained 
hy  exposure  to  100°C  for  20  minutes  after  12,14  and  17  days  dessica- 
tion.  As  a result  of  this  constantly  changing  resistance  of  the  corn 
to  heat,  much  of  my  early  work  was  of  little  value,  except  to  indi- 
cate the  proper  tine  and  temperature  to  use  for  corn  desiccated  the 
same  length  of  time.  Hence  the  need  for  a succession  of  desiccations 
in  order  to  get  significant  results* 

It  is  very  evident  from  Table  IX,  that  corn  desiccated  “2"  days,  con- 
taining 8.78  percent  moisture,  and  killed  at  90°C  for  20  minutes,  is 
very  much  less  resistant  to  heat  than  corn  desiccated  23  days,  con- 
taining 5.75  percent  moisture,  and  giving  a germination  of  63.3  per- 
cent after  90°C  for  3|-  hours  (225  minutes).  Similarly  corn  killed  at 
100°C  for  30  minutes  containing  6.11  percent  moisture  after  14  days 
desiccation,  is  much  less  resistant  than  corn,  containing  2.16  per- 
cent moisture  after  100  days  desiccation,  giving  63.3  percent  germi- 
nation after  exposure  to  100°C  for  2£  hours  (150  minutes).  This  re- 
lation existing  throughout  the  table  justifies  me  in  saying  that, 
without  regard  to  the  type  of  corn  used  the  resistance  of  corn  to 
heat  varies  inversely  as  its  moisture  content  at  the  time  of  heating. 

Probably  the  most  significant  fact  brought  to  light  by  the  desic- 
cation study  is  the  varied  response  of  the  different  types  of  corn 


-37- 

to  the  treatment.  Beginning  with  the  first  day  of  desiccation  and 
continuing  throughout,  (100  days),  the  percent  of  germination  of  PCB 
after  heating  is  much  higher  than  either  Box  or  PCG , while  Pox  is 
somewhat  lower  than  PCG,  which  occupies  an  intermediate  position 
throughout.  The  averages  of  Table  IX  are  brought  together  in  Table  X 
and  make  these  differences  more  evident. 


Table  X 

. Averages  of 

Percent 

of  Germination  of  Bes 

iccated 

Corn. 

Types 

of 

Corn 

Bays 

of  Besiccation 

L Bay 

2 Bays 

4 Bays 

6 Bays 

8 Bays 

9 Bays 

10  Bays 

12  Bays 

14  Bays 

PCB 

92.5 

42.0 

86.1 

77.5 

86.3 

86.6 

90.0 

60.9 

46.8 

Pox 

75.0 

60.0 

86.1 

46.3 

57.1 

56.6 

55.0 

35.5 

22.9 

PCG 

79.5 

52.0 

61.1 

55.0 

79.4 

70.0 

77.5 

42.7 

36.4 

Types 

15  D 

17  B 

20  B 

23  B 

27  B 

31  B 

100  B 

Average 

PCB 

66.7 

42.5 

87.5 

76.7 

64.5 

78.7, 

63.3 

71.8 

Pox 

0 

5.0 

67.5 

38.9 

24.5 

23.3 

80.0 

48.7 

PCG 

3.3 

7.5 

72.5 

28.9 

34.5 

59.8 

43.3 

50.2 

< 


-38- 

Using  the  percent  of  germination  of  PCG  as  zero,  the  difference 
between  PCB  and  PCG  is  plotted  in  Fig.  9 as  a solid  line  while  the 

difference  between  Fox  and  PCG  is  plotted  as  a broken  line.  Thus  at 
12  days,  PCB  has  a germination  18.2  percent  higher  than  that  of  PCG, 
hence  it  is  plotted  as+18.2,  while  Fox  has  a germination  of  7.2 

percent  lower  than  PCG,  hence  it  is  plotted  as  -7.2.  In  only  one 
instance,  (2  days)  does  PCB  have  a lower  germination  than  PCG  and 
Fox  a greater  germination  than  either,  while  Fox  quite  consistently 
shows  a lower  germination  than  PCG,  though  not  as  much  lower  than 

PCG,  as  PCB  is  higher. 

The  average  of  all  germinations  of  desiccated  corn  are;  PCB-71.8, 
Fox-48.7,  and  FCG-50.2  percent. 

The  difference  in  germination  in  favor  of  PCB  is  most  visible 
where  the  temperatures  are  highly  injurious;  as  for  example:  the 
90°C  series  at  15  days,  the  100°C  and  90°C  series  at  17  days,  and 
the  100°C  series  at  27  days,  where  almost  complete  killing  occured 
in  both  PCG  and  Fox  while  PCB  gave  a fair  percent  of  germination. 

The  differences  are  not  so  great  in  series  such  as  that  of  80°C  at 
4 days,  where  the  time  of  heating  was  not  long  enough  to  be  injurio 
and  the  differences  may  even  be  in  favor  of  PCG  or  Fox,  where  very 
little  heat  is  applied,  due  probably  to  the  superior  vitality  of  PCG 
when  not  affected  by  too  high  a temperature.  This  may  be  seen  in 
90°C  for  5 minutes  after  2 days  desiccation  and  in  100°C  for  5 min- 
utes after  12  days  desiccation  and  in  many  others  not  included  in 
the  table,  such  as  a series  at  80°C  for  10-35  minutes  after  2 days 
desiccation  where  the  average  percent  of  germination  was;  PCB-80, 
Fox-88,  and  PCG-92;  10-35  minutes  being  altogether  too  short  a time 
to  produce  injury. 


G e /P/w/  /v'  a Tv  on/. 


-41- 

Table  XI  brings  together  the  average  plumule  lengths  of  the  corn 
treated  after  desiccation.  Although  it  does  not  in  all  cases  follow 

Table  X yet  the  relative  ranking  of  the  types  is  very  similar  to 
that  of  the  percents  of  germination.  The  average  of  all  plumule 
lengths  shows  that  PCB  corn  has  the  greatest  plumule  length,  Fox  the 
least,  and  PCG  intermediate,  thus  having  the  same  ranking  as  the  per- 
cent of  germination. 

Some  difference  of  opinion  has  existed  and  probably  still  exists, 
concerning  the  effects  of  desiccation  on  the  viability  of  seeds. 

Some  investigators,  notably  Ewart  (1897),  have  held,  that  it  is  im- 
possible to  reduce  the  moisture  content  of  the  seed  much  below  2 to 
3 percent  of  air-dry  weight  without  affecting  germination  injurious- 
ly. In  the  face  of  more  recent  work  it  is  impossible  to  hold  to 
this  opinion  concerning  all  seeds.  The  work  of  Waggoner  (1917)y 
Ha.rrington  and  Crocker  (1918)  and  Walker  (1922)  have  shown  that  some 
seeds  can  be  reduced  to  a very  low  moisture  content  without  injury 
to  their  viability.  The  work  of  earlier  investigators  along  this 
line,  has  been  reviewed  by  Harrington  and  Crocker  (1918)  and  need 
not  be  reviewed  here.  In  their  own  work  they  carefully  dried  sever-  j 
al  kinds  of  seeds,  in  vacuo  over  CaO  and  over  concentrated  sulphuric^ 
acid.  They  reduced  the  moisture  content  of  Kentucky  blue  grass  seed!; 
to  0.1  percent  and  then  heated  it  for  6 hours  at  100°C , reducing  it 
still  more.  The  seed  thus  treated  gave  a slightly  lower  germination 
(5  percent)  though  its  germination  energy  was  considerably  reduced. 
The  germination  of  barley  and  Sudan  grass  was  not  lowered  by  drying 
though  the  moisture  content  was  reduced  to  0.5  and  0,6  percent, 
Johnson  grass  was  slightly  injured  by  being  dried  to  a moisture  con- 
tent of  0.1  percent.  Wheat  with  moisture  content  reduced  to  0.9% 
was  not  injured. 


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. 


. 


MOISTURE  DETERMINATIONS 


-43- 

In  order  to  know  definitely  the  amount  of  moisture  present  in  the 
corn  used  and  the  exact  effect  of  drying  on  this,  it  was  necessary 
to  make  a series  of  moisture  determinations  of  air-dry  corn, and  that 
dried  for  various  periods  of  time.  Two  determinations  wrere  made  in 
November  by  the  Division  of  Crop  Production  on  100  gram  samples, 
using  the  Duvel  method,  resulting  in;  Fox-10.4  percent  and  PCG-10.0 
percent.  All  subsequent  determinations  were  made  by  placing  the 
corn  (10  kernels)  in  weighed  aluminum  dishes  and  reducing  to  con- 
stant weight  in  an  electric  drying  oven  at  100°C.  Because  of  a 
slight  variation  in  temperature  between  the  two  shelves  of  the  oven, 
it  was  attempted  to  keep  all  samples  on  the  same  shelf  to  do  away 
with  any  error  which  might  exist,  due  to  that  cause.  The  dishes 
were  cooled  in  a calcium  chloride  desiccator  and  weighed  at  intervals 
of  1 day  until  found  constant  in  weight.  This  frequently  took  as 
long  as  10  days. 

Table  XII.  Moisture  Determinations  of  Corn,  Air-Dry 


and  Desicca/ted 


Time  of 

desiccation  in 

days. 

Type 

AIR-DRY 

1 Day 

2 Days 

4 Days  6 Days 

8 Days 

10  Days 

14  Days 

17  Day 

PCB 

10.93 

8.87 

8.09 

7.87 

7.28 

7.49 

6.19 

5.98 

5.70 

Fox 

10.64 

8.77 

8.97 

7.79 

7.74 

7.56 

6.46 

6.32 

6.28 

PCG 

10.41 

9.23 

9.28 

7.70 

8.43 

7 . 22 

7.73 

6.05 

6.87 

Type 

20  Days  25  D 

27  D 

72  D 

82  D 

100  D 

115  if 

115  D^ 

115  Df 

PCB 

6.60 

5.53 

5,02 

3.76 

2.88 

2.23 

2.20 

2.05 

0.73J* 

Fox 

5.94 

5.77 

4.69 

3.32 

3.00 

1.92 

2.37 

• • • • 

1.19 

PCG 

5.79 

Ju9£-.. 

6.30 

3.04 

3.17 

2.40 

2.45 

2.35 

1.16 

*-70°C-30  hrs . T- 
t*-Des.  117  days, 

70°-60 

70°-60 

hrs . 
hrs , 

£-70°-60  hrs, 
98°-32  hrs. 

98°- 20  hrs. 

-44- 


In  Table  XII  are  given  the  moisture  determinations  made  on  the 
air-dry  and  desiccated  corn.  Tne  figures  are  based  on  single  deter- 
minations, except  air-dry  - 5 determinations , and  8 and  10  days  - 2 
determinations  each.  The  moisture  is  expressed  in  percents,  based 
on  the  air-dry  weight,  and  not  on  the  dry  weight. 

Reducing  Table  XII  to  a graph,  (Figure  10)  the  moisture  relations! 
of  the  three  types  of  corn  can  best  be  expressed  by  showing  relative 
water  loss  after  different  periods  of  desiccation,  up  to  27  days. 

The  moisture  contents,  of  the  three  types  of  corn,  after  72,  82  and 
100  days  of  desiccation  is  shown  at  the  right  of  the  graph.  It  will 
be  noted  that  there  is  a fairly  steady  decrease  in  the  moisture  con- 
tent. PCB  contains  the  most  moisture  in  the  air-dry  condition  but 
soon  falls  to  the  least  and  remains  there  fairly  constantly;  PCG 
contains  the  least  moisture  in  the  air-dry  condition  but  rises  to 

the  most,  and  Fox,  maintains  an  intermediate  position. 

The  15  moisture  determinations,  from  1 to  115  days,  inclusive, 
given  in  Table  XIII  may  be  grouped  according  to  frequency.  That  is, 
the  number  of  times,  out  of  these  15,  that  each  type  of  corn,  con- 
tains the  least,  medium  and  most  amounts  of  moisture. 

This  results  in: 

Least  Medium 
PCB  8 4 

Fox  3 10 

PCG  4 1 

This  is  graphically  shown  in  Figure  11,  the  black  spaces  indicating 
the  number  of  times  each  type  of  corn  contains  the  least;  the  clear 
spaces,  the  medium  amount,  and  the  cross-hatched  spaces,  the  great- 
est amount  of  moisture. 


Most 

3 

2 

10 


The  differences  in  amount  are  not  large  however,  the  average  of 


-45- 


all  desiccations  "being;  FCB-5.71  percent,  Fox-5.79  percent  and  PCG- 
6.11  percent,  giving  differences  of  .08  and  .32  percent  respectively. 


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-47- 


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GRADIENT  OF  DESICCATION. 

In  the  process  of  desiccation,  wii-h  the  corn  in  long  wire  baskets 
suspended  over  acid  and  with  the  bottom  of  the  basket  within  15  mm. 
of  the  surface  of  the  acid  and  the  top  within  115  mm.  of  the  surface, 
it  seemed  natural  to  question  whether  desiccation  was  exactly  uni- 
form throughout  the  column  of  corn.  In  view  of  the  methods  some- 
times used  to  secure  moisture  or  desiccation  gradients  over  water, 
salt  solutions,  or  mixtures  of  sulphuric  acid  and  water  in  open 
vessels , it  was  necessary  to  determine  whether  complete  uniformity 
of  desiccation  occured  throughout  a tightly  closed  vessel.  The  same 
paraffined  wire  baskets  as  in  desiccation  were  used  and  only  PCB 
corn  experimented  with.  These  desiccators  were  placed  in  a 30°C  con- 
stant temperature  case  and  the  corn  used  after  8,9,  12  and  16  days 
desiccation.  When  ready  for  treatment,  the  corn  was  divided  into 
3 parts  by  sticking  short  pieces  of  copper  wire  thru  the  column  of 
corn  at  the  proper  places  until  they  formed  a network  which  held  the 
corn  so  the  upper  1/3  could  be  removed.  Each  third  was  then  placed 
in  wire  baskets  in  desiccators  so  it  would  not  absorb  moisture  while 
being  tested.  Each  third  made  about  12  lots  of  10  kernels  each 
which  were  tested  at  the  proper  temperature  for  periods  of  time  known 
to  be  injurious.  Thus  after  16  days  desiccation,  each  third  of  cornj 
was  heated,  10,  11,  12,  and  so  on  up  to  22  minutes.  Corn  desiccated; 
8,9  and  12  days  was  heated  at  90°C  while  corn  desiccated  16  days 
was  heated  at  100°C. 

The  results  of  these  series  are  summarized  in  Table  XIII. 


. 

. . 


« « 


, 


. 

. 


. 


, 

< 

. 


1 


Table  XIII.  Desiccation  Gradient  of  PCB  Corn 

Summary . 


---  = 

Position 

in 

Desiccator 

Percent  of  Germination 

Length  of 

Desiccation  in  Days. 

8 

9 

12 

16 

Average 

Upper 

84.0 

70.9 

35.5 

70.8 

65.3 

Middle 

75.0 

63.3 

37.7 

68.5 

63.6 

Lower 

66.0 

60.0 

32.2 

68.5 

56.6 

Ratio  of  Upper 

to  Lower 

18.0 

10.9 

3.3 

2.3 

8.7 

Position 

Length  of  Plumule  (in 

mm. ) 

in 

Length  of 

Desiccation  in  Days 

Desiccator 

8 

9 

12 

16 

Average 

Upper 

78.0 

67.1 

59.3 

78.8 

70.8 

Middle 

73.0 

60.0 

69.0 

79.2 

70.3 

Lower 

72.0 

70.6 

53.6 

75.2 

67.9 

Ratio  of  Upper 

6.0 

3.5 

6.3 

3.6 

2.9 

to  Lower 

-50- 


From  the  data  in  Table  XIII  it  is  evident,  that  the  corn  from 
the  upper  1/3  of  the  basket,  which  was  furthest  from  the  surface  of 
the  acid,  was  the  most  resistant  to  heat,  and  that  from  the  lower 
1/3,  closest  to  the  acid,  was  least  resistant.  To  reduce  to  a single 
figure  the  difference  in  germination  between  the  upper  and  lower 
parts,  the  percent  of  germination  of  the  lower  was  subtracted  from 
that  of  the  upper  and  the  figures  given  at  the  foot  of  each  section 
of  the  table.  These  figures  indicate  that  after  6 days  desiccation 
the  corn  in  the  upper  1/3  gave  18.0  percent  better  germination  after 
heating,  than  that  in  the  lower.  With  increased  desiccation,  this 
difference  became  less  until  after  16  days  it  was  only  2.3  percent. 
It  is  probable  that  it  would  slowly  approach  zero  as  a limit  sc  that 
with  time  the  desiccation  would  become  uniform  throughout.  Data  are 
not  available  to  indicate  what  the  ratio  would  be  following  1 to  8 
days  desiccation,  but  it  is  probably  that  it  would  describe  a regu- 
lar curve,  there  being  little  difference  after  a short  period  of 
drying,  this  difference  increasing  rapidly  to  a climax  and  then 
slowly  decreasing  again  to  zero. 

The  length  of  plumule  varies  more  widely,  as  is  usual,  but  the 

averages  rank  the  same  as  the  percents  of  germination.  The  ratio 
of  upper  to  lower  shows  little  difference  throughout  the  series, 
but  its  average  is  in  favor  of  the  upper  by  2.9  mm. 

As  the  same  amount  of  corn  was  used  from  each  of  the  baskets  at 
each  test  (in  testing  resistance  after  desiccation),  the  top  of  the 
column  of  corn  was  approximately  the  same  distance  from  the  surface 
of  the  acid,  therefore,  the  error  introduced  by  a difference  in 
height  above  the  desiccating  surface  would  be  negligible. 

One  kind  of  corn  (PCB)  only,  being  used,  the  difference  in  be- 
havior of  the  upper  and  lower  parts  of  the  basket  must  be  due  to 


. 


, 


, ' 


, 

, 


. 


, 

* 


, 


-51- 


differences  in  moisture  content.  To  determine  what  difference  exist- 
ed, moisture  determinations  were  made  of  corn  from  the  upper,  middle 
and  lower  parts  of  the  basket,  with  the  following  results: 

Upper  5.70  percent 

Middle  6.03  percent 

Lower  6.30  percent 

This  gives  a difference  cf  .60  percent  in  favor  of  the  upper,  which 
further  supports  the  statement  that  the  resistance  of  corn  to  high 
temperatures  varies  inversely  as  its  water  content  at  the  time  of 
heating . 


. 

. 

: 

im  i . 

. 


-52- 

DAILY  VARIATION. 

It  was  readily  noticeable,  in  the  heating  tests,  that  varying  re- 
sults were  obtained  on  successive  days,  even  tho  the  same  type  of 
corn,  the  same  heat,  and  the  same  period  of  exposure  was  used.  This 
seemed  to  be  correlated  with  climatic  conditions  out-of-doors-humidi- 
ty,  and  as  the  ventilators  in  the  laboratory  were  open  part  of  the 
time,  the  laboratory  air  varied  in  humidity  also.  To  simulate  con- 
ditions under  which  corn  would  be  stored  in  open  cribs  on  the  farms 
of  Illinois,  shelled  corn  of  the  three  types  was  placed  in  wire  bas- 
kets and  hung  out-of-doors,  under  a roof-like  shelter  suspended  on 
a wire  strung  between  two  wings  of  the  greenhouse,  and  open  to  all 
air  currents,  but  protected  from  direct  sunshine  and  from  rain. 

Tests  made  on  this  corn  at  this  season  of  the  year  will  serve  as  a 
guide  in  treating  crib  corn  during  the  rainy  spring  season,  for 
fungous  or  insect  pests  by  means  of  heat,  and  give  the  limits  of 
time  and  temperature  beyond  which  injury  to  germination  would  result 
Furthermore  it  was  desireable  to  find  out  if  the  variation  in  the 
same  test  from  day  to  day  was  due  to  variation  in  relative  humidity 
of  the  air,  and,  if  so,  how  rapidly  and  to  what  extent  this  varia- 
tion in  moisture  content  followed  the  variations  in  humidity.  The 
variation  in  moisture  content  of  the  corn  was  not  measured  directly 
but  was  measured  by  the  variation  in  percent  of  germination  follow- 
ing heat  treatment,  a low  germination  indicating  a high  relative 
humidity,  hence  much  moisture  in  the  corn,  and  vica  versa. 

A check  test  was  made  on  the  air-dry  corn  just  before  it  was  hung 
out-of-doors  (on  March  28)  and  at  intervals  afterward  up  to  April 
26.  Each  test  consisted  of  a check  and  10  kernels  of  each  type  of 
corn  heated  at  90°C  for  3, 4, 5, 6, 7, 8,  and  9 minutes.  The  percent  of 


* 

, 

. 


' 


. 


. 


, 


I 


. 


' t t c • 


-53- 

germination  of  each  type  of  corn  after  these  exposures  were  added  and 
these  totals  used  to  construct  the  graph  shown  in  Figure  12.  Thus  on 
April  2,  PCB , Fox  and  PCG  corn  from  the  baskets  hanging  out-of-doors 
was  tested  at  90°C  with  the  following  result  in  germination: 


3 4 5 6 7 8 9 


Check 

Min, 

Min. 

Min. 

Min. 

Min. 

Min, 

Min. 

Total 

PCB 

100 

100 

70 

50 

40 

0 

0 

0 

260 

Fox 

100 

90 

90 

80 

30 

0 

0 

0 

290 

PCG 

100 

90 

70 

60 

30 

0 

0 

0 

250 

The  total  does  not  include  the  check,  which  did  not  vary. 

This  was  done  at  each  test  and  these  totals  are  summarized  in  Table 
XIV. 


Table  XIV.  Totals  of  Germination  - Daily  Variation, 


March 

Aioril 

Type  of 
Corn 

Check 

28 

29 

30 

1 

2 

5 

6 

8 

9 

11 

PCB 

390 

1 250 

210 

210 

260 

120 

130 

180 

140 

130 

Fox 

430 

300 

280 

290 

290 

210 

180 

140 

230 

180 

PCG 

430 

340 

280 

240 

250 

130 

180 

90 

220 

270 

Average 

417 

297 

257 

247 

267 

153 

163 

137 

197 

193 

Type  of 
Corn 

12 

15 

16 

17 

19 

20 

22 

23 

24 

26 

PCB 

200 

180 

120 

180 

220 

160 

180 

200 

203 

140 

Fox 

250 

250 

230 

180 

240 

270 

280 

340 

260 

200 

PCG 

220 

220 

160 

230 

220 

230 

200 

260 

290 

170 

Average 

223 

217 

170 

197 

227 

220 

220 

267 

251 

153 

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-54- 

The  data  on  relative  humidity  was  obtained  from  the  Division  of 
Soil  Physics.  In  this  Division  daily  relative  humidity  readings  are 
taken  at  7 A.M.,  2 P.M.  and  7 P.M.  My  heating  tests  were  not  made 
coincident  with  the  observed  readings  but  the  nearest  humidity  read- 
ing was  taken  as  the  one  to  be  graphed.  Thus  if  the  corn  was  tested 
at  3 P.M.  on  April  2,  the  relative  humidity  reading  taken  on  that 
day  at  2 P.M.  was  the  one  used. 

In  Figure  12,  the  red  line  indicates  the  relative  humidity  and 
the  black  line  the  average  of  the  total  germinations.  It  was  found, 
upon  graphing  the  germination  totals  for  each  type  of  corn  separate- 
ly, that  no  type  followed  the  changes  in  relative  humidity  more 
closely  than  another.  For  the  sake  of  clearness,  therefore,  the 
totals  for  the  three  types  were  averaged  and  the  graph  made  from 
this  data.  The  variation  of  the  three  types  followed  that  of  the 
relative  humidity  closely  where  the  changes  were  great  and  continued 
for  several  days,  such  as  the  big  drop  from  April  2-5  and  the  drop 
from  April  23-26,  but  where  the  changes  were  smaller  and  less  pro- 
longed, as  April  11  and  12,  one  type  would  follow  the  change  in  re- 
lative humidity  while  the  other  two  types  would  vary  in  the  opposite 
direction,  or  vica  versa. 

We  are  not  justified,  from  the  data  at  our  disposal,  therefore, 
in  saying  that  one  type  varies  more  widely  or  more  rapidly  under 
out-door  conditions  than  another.  But  we  can  say;  that,  with  few 
exceptions,  the  average  resistance  to  heat  of  corn  stored  in  the  ope: 
changes  inversely  as  the  changes  in  relative  humidity  of  the  atmos- 
phere. The  places  where  the  curves  do  not  coincide  the  differences 
are  not  great  and  could  probably  be  explained  by  a wide  change  in 
humidity  before  the  test  was  made, or,  probably  better,  by  the  corn 
lagging  behind  the  changes  in  relative  humidity  of  the  atmosphere. 


->55- 

The  germination  totals  of  PCB  were  low,  those  cf  PCG , high,  and 
thoee  of  Fox  intermediate.  This  relation  held  quite  consistently 
throughout  the  entire  test. 

A graph  of  the  average  total  plumule  lengths  varied  more  widely 
than  did  that  of  the  percent  of  germination  and  did  not  follow  the 
changes  in  relative  humidity  as  closely  as  did  that  of  the  percent 
of  germination,  hence  was  not  included  in  Figure  12. 

A moisture  determination  was  made  on  April  26,  at  the  time  the 
test  was  made.  The  day  was  warm  and  humid  and  the  corn  fell  on  the 
table  with  a dull  thud,  while  being  handled.  From  the  graph  we  see 
the  humidity  was  low,, but  not  the  lowest  reached  during  the  test.  The 
moisture  determination  was  as  follows: 

PCB  - 14.86  percent 
Fox  - 14.60  percent 
PCG  - 14.44  percent 

This  bears  our  the  statement  that  PCB,  in  the  air-dry  condition, 
contains  the  most  moisture  and  Fox  and  PCG  lesser  amounts  in  the 
order  named.  The  average  total  germination  on  this  day  was  one  of 
the  lowest  in  the  table. 


-56- 


PLACINC-  III  WATER  AFTER  HEATING. 

Just  (1875)  in  working  with  seeds  of  Trifolium  pratense  said  that 
seeds  heated  at  100°C  germinated  if,  after  heating,  they  were  sup- 
plied with  water  slowly,  hut  did  not  germinate  if  supplied  with  water 
rapidly.  An  extensive  series  of  experiments  were  undertaken  to  see 
if  placing  in  water  immediately  after  heating  to  high  temperatures 
had  any  effect  on  the  germination  of  corn.  Whether  the  sudden  in- 
take of  water  and  the  sudden  cooling  injured  the  viability  of  the 
kernels. 

The  corn  was  heated  in  phials  in  duplicate  sets  and  immediately 
after  heating,  while  the  phials  were  still  hot,  the  corn  from  one 
set  was  placed  in  tap  water  at  room  temperature , while  the  corn  from 
the  other  set  was  placed  in  the  aluminum  dishes  to  cool.  After  the 
first  set  had  soaked  4 hours  they  were  taken  out  and  placed  between 
moist  blotting  paper,  to  prevent  drying  out,  and  the  second  set 
soaked  for  4 hours,  thus  soaking  each  set  for  an  equal  period  of 
time.  At  the  end  of  the  second  4 hours  both  Bets  were  placed  in  wet 
rag  dolls  and  these  placed  in  the  germinator  jars  as  usual.  Two 
trials  were  made,  involving  air-dry  corn  heated  at  80°  and  90°C , 
corn  which  had  been  desiccated  19  days  heated  at  90°C  and  corn  which 
had  been  desiccated  18,  51,  86  and  100  days,  heated  at  100°C , The 
entire  result  may  be  summarized  in  Table  XV.  Air-dry  corn  was 
averaged  separately  from  desiccated  to  determine  any  difference  in 
resistance,  S - designates  corn  placed  in  water  immediately  after 
cooling  and  D - corn  placed  in  aluminum  dishes  to  cool. 


-57- 

Table  XV.  Effect  of  Placing  in  Water 
Immediately  after  Heating. 


Type 

of 

Corn 

First 

Trial 

Second  Trial 

Air -Dry 

Desiccated 

Air-Dry 

Desiccated 

S 

D 

S 

D 

S 

D 

S 

D 

PCB 

91.7 

86.6 

87.7 

91.1 

56.7 

53.3 

81.8 

71.0 

Fox 

95.3 

88.3 

53.9 

51.4 

60.0 

58.3 

46.7 

51.7 

PCG 

90.6 

85.0 

58.3 

63.3 

46.7 

53.3 

49.2 

46.7 

Average 

91.9 

86.6 

66 .6 

68.6 

54.5 

55.0 

59.2 

56.5 

Length  of 
Plumule 
, . . . — 

113.0 

118.4 

72. 2 

27.6 

72.8 

63.4 

72.3 

83.5 

Prom  Table  XV  it  is  evident  that  there  is  no  consistent  variation 
due  to  placing  in  water  after  heating.  In  the  first  trial;  in  air- 
dry  corn,  the  germination  was  best  in  that  placed  in  water  immediate- 
ly after  cooling,  and  the  plumule  length  was  least.  In  desiccated 
corn,  the  germination  was  best,  in  that  placed  in  aluminum  dishes  to 
cool,  and  the  length  of  plumule  was  least.  This  is  exactly  reversed 
in  the  second  trial.  The  differences,  moreover,  were  not  large. 

We  may  say,  therefore,  that  placing  corn  in  water  immediately  after 
heating  has  no  effect  whatever  on  either  the  percent  of  germination 
or  the  length  of  plumule. 


-58- 


GROWTH  IN  SOIL, OP  HEATED  CORN. 

To  determine  the  effect  of  heating  the  kernels  upon  the  germina- 
tion of  corn  in  soil  and  the  subsequent  growth  and  green  weight  of 
the  seedling,  corn  of  the  three  types  was  heated  and  then  planted  in 
rows  2x5  inches,  in  garden  loam  in  a bench  in  the  middle  of  the  gree* 
house,  equally  lighted  and  heated  from  all  sides.  Air-dry  corn  was 
heated  at  80°C  for  5,  7-J,  10,  12J-  and  15  minutes  and  was  planted  -f 
inch  deep.  Corn  which  had  been  in  the  desiccator  for  16  days  was 
heated  at  90°C  for  110,  120,  130,  140  and  150  minutes  and  was  planted 
the  same  way.  Checks  of  each  were  also  planted.  Ten  kernels  of  eac? 
type  were  used  for  each  period  of  heating. 

There  was  a noticeable  retardation  in  the  growth  of  corn  heated 
most  severely,  in  both  the  air-dry  and  the  desiccated  lots.  In  dig- 
ging up  the  kernels  there  were  many  which  had  put  out  a short  plu- 
mule or  radicle  but  did  not  have  growth  energy  enough  to  force  their 
way  to  the  surface.  This  probably  accounts  for  much  of  the  differ- 
ence between  the  results  obtained  in  rag  dolls  and  that  obtained  in 
the  soil,  for  the  percent  of  germination  in  rag  dolls  was  60.0  per- 
cent and  in  soil,  27.8  percent,  in  a series  using  air-dry  corn  heat- 
ed at  80°C.  Records  were  taken  of  the  time  of  appearance  of  the 
shoots  above  the  soil,  and  height  measurements  were  taken  at  the  end 
of  30  days,  at  which  time  the  plants  were  harvested  by  cutting  off 
the  stalk  at  the  surface  of  the  soil  and  the  green  weight  taken. 

The  results  of  the  above  planting  are  recorded  in  Tables  XVI  and 


XVII 


Table 

XVI.  Growth 

-59- 

of  Heated  Corn  in  Soil-Air -Dry-80°C . 

Treatment 

Type 

Percent  of 

Total  green 

Average  green 

Height  per 

Germinat ion, 

Weight 

weight  per 

plant 

(grams) 

plant  (grams' 

(cm. ) 

Check 

PCS 

100 

47.85 

4.785 

59 

Fox 

100 

37.65 

3.765 

59 

PCG 

90 

40.25 

4.472 

56 

5 Min. 

PCB 

100 

43.00 

4.300 

62 

Fox 

70 

23.10 

3.300 

55 

PCG 

90 

41.97 

4.663 

57 

7-5-  Min. 

PCB 

100 

40.10 

4.010 

54 

Fox 

70 

31.23 

4.461 

52 

PCG 

100 

55.97 

5.597 

64 

10  Min. 

PCB 

60 

6.95 

1.158 

30 

Fox 

60 

29.32 

4.887 

61 

PCG 

60 

14.98 

2.497 

43 

12-g-  Min. 

PCB 

10 

0.81 

0.810 

28 

Fox 

10 

0.52 

0.520 

24 

PCG 

50 

7.65 

2.550 

37 

15  Min 

PCB 

0 

0 

0 

0 

Fox 

0 

0 

0 

0 

PCG 

0 

0 

0 

0 

Average 

PCB 

67.5 

22.72 

2.570 

43.5 

Fox 

52.5 

21.04 

3.292 

48.0 

PCG 

70.0 

30.14 

3 . .8.27 

5.0.3 

-60- 

Table  XVII.  Growth  of  Heated  Corn  in  Soil- 
Desiccated  16  days  - 90°C. 


Treatment 

Type 

Percent  of 
Germination 

Total  Green 
Weight 
(grams) 

Average  Green 
Weight  per 
plant 
(grams) 

Height  per 
plant 
(cm. ) 

Check 

PCB 

100 

39.70 

3.970 

53 

Fox 

80 

29.35 

3.670 

49 

PCG 

100 

39.25 

4.242 

51 

110  Min. 

PCB 

70 

16.95 

2.421 

43 

Fox 

10 

2.00 

2.000 

40 

PCG 

0 

0 

0 

0 

120  Min. 

PCB 

90 

33.10 

3.678 

48 

Fox  • 

0 

0 

0 

0 

PCG 

0 

0 

0 

0 

130  Min. 

PCB 

60 

10.00 

1.667 

34 

Fox 

10 

0.47 

0.470 

21 

PCG 

0 

0 

0 

0 

140  Min. 

PCB 

60 

9.80 

1.633 

30 

Fox 

0 

0 

0 

0 

PCG 

10 

3.00 

3.000 

43 

150  Min. 

PCB 

70 

14.90 

2.129 

38 

Fox 

0 

0 

0 

0 

PCG 

0 

0 

0 

0 

Average 

PCB 

16.95 

2.764* 

Fox 

4.0 

4.92 

1 . 235* 

12.2 

PCG 

2.0 

.60 

3.000* 

8.6 

^Average  of  those  plants  that  grew. 


-61- 

In  the  air-dry  corn  (Table  XVI)  no  germination  resulted  from  the 
15  minute  heating.  PCG  corn  consistently  had  a higher,  percent  of 

germination,  total  green  weight,  average  green  weight  per  plant  and 
height  per  plant,  Pox  varied  widely  being  high  in  average  green 
weight  per  plant  and  height  per  plant,  but  low  in  germination  and 
total  green  weight.  This  was  probably  due  to  the  fact  that  Fox  fre- 
quently had  a few  highly  resistant  kernels  which  produced  large  plant! 
This  is  even  more  noticeable  in  Table  XVII,  where,  at  temperatures 
which  killed  practically  all  the  kernels,  Fox  occasionally  sent  up  a 
fairly  vigorous  seedling.  The  inherent  weakness  of  Fox  is  shown 
by  its  low  germination.  PCB  was  high  in  germination  and  total  green 
weight  but  low  in  average  green  weight  per  plant  and  height  per  plant 

In  Table  XVII  we  have  the  reverse  of  Table  XVI.  It  is  an  extreme 
example  of  the  superior  resistance  to  heat  of  PCB  after  desiccation. 
This  is  shown  especially  in  the  percent  of  germination.  An  occasion- 
al resistant  kernel,  especially  in  Fox,  but  also  in  PCG,  sent  up  a 
seedling  even  after  severe  treatment.  PCB  shows  remarkable  germina- 
tion throughout.  The  average  height  per  plant  was  much  greater  in  . 
PCB  and  where  only  those  plants  that  grew  are  averaged  we  have: 
PCB-38.6  cm.,  Fox-30.5  cm.,  and  PCG-43.0  cm.  This  same  ratio  holds 
in  green  weight  per  plant. 


-62- 

V . CONCLUSIONS . 

1.  Air-dry  corn,  containing  10-11$  moisture  is  killed  by  exposure  to 

80°C  and  90°C  for  25  and  10  minutes  respectively  and  is  in- 
jured by  exposure  to  70°,  80°  and  90°C  for  80,  10  and  5 
minutes  respectively. 

2.  Under  air-dry  conditions,  the  apparently  diseased  corn  (PCB)  con- 

tains the  most  moisture,  apparently  disease-free  (PCG)  the 
least  moisture  and  the  badly  diseased  (Fox)  an  intermediate 
amount.  The  resistance  to  heat  is  inversely  proportional 
to  their  moisture  content. 

3.  The  resistance  of  corn  to  high  temperatures  varies  inversely  as 

its  water  content  at  the  time  of  heating. 

4.  After  desiccation  over  sulphuric  acid  the  apparently  diseased  corr 

(PCB)  contains  the  least  moisture,  apparently  disease-free 
(PCG)  the  most  moisture  and  the  badly  diseased  (Fox)  an 
intermediate  amount. 

5.  After  desiccation  the  apparently  diseased  corn  (PCB)  is  very 

much  more  resistant  to  heat;  compared  with  apparently 
disease-free  (PCG)  and  badly  diseased  (Fox)  corn,  than  its 
slightly  less  moisture  content  would  indicate.  This  great- 
er resistance  becomes  evident  only  as  the  temperatures  be- 
come injurious. 

6.  After  desiccation,  apparently  diseased  corn  (PCB)  is  very  resist- 

ant to  heat,  apparently  disease-free  (PCG)  less  resistant, 
and  badly  diseased  (Fox)  is  least  resistant  in  spite  of 
its  moisture  content  being  less  than  that  of  apparently 
disease-free  corn  (PCG).  This  last  difference  may  be  ex- 
plained by  the  superior  vigor  of  apparently  disease-free 
(PCG)  and  the  diseased  weakened  condition  of  badly  diseas- 
ed (Fox) . 

7.  Desiccation  brings  about  changes  in  the  corn  which  cause  apparent- 

ly diseased  (PCB)  to  become  very  resistant  to  heat  and 
causes  badly  diseased  (Fox)  to  become  less  resistant. 

What  these  changes  are  is  not  known. 

8.  Desiccation  over  sulphuric  acid  in  a closed  vessel  is  not  uniform 

being  greatest,  farthest  from  the  surface  of  the  acid,  and 
least,  closest  to  it.  This  gradient  gradually  lessens  as 
the  length  of  desiccation  increases. 

9.  The  resistance  to  heat  of  air-dry  corn,  both  in  the  laboratory 

and  out-of-doors,  varies  with  the  variations  in  climatic 
conditions-humidity.  The  three  kinds  of  corn  tested  vary 
essentially  alike. 

10.  Placing  the  heated  corn  in  water  immediately  after  treatment  has 
no  injurious  effect  on  its  viability. 


. . 


. 


- 


, 


-63- 

11.  Germination  of  heated  corn  is  better  in  rag  dolls  than  in  soil. 


12,  Growth  follows,  in  general,  the  degree  of  viability  of  the  treat- 

ed and  untreated  corn. 

13.  The  percent  of  germination , green  weight  and  height  of  plants, 

grown  in  soil,  from  heated  corn,  parallels  the  behavior 
shown  in  germination.  In  air-dry  corn  apparently  disease- 
free  (PCG)  is  consistently  highest,  with  apparently  diseas- 
ed (PCB)  lowest, and  badly  diseased  (Fox)  intermediate. 

In  desiccated  corn,  apparently  diseased  (PCB)  is  consist- 
ently highest,  apparently  disease-free  (PCG)  usually  low- 
est, and  badly  diseased  (Fox)  varies  between  lowest  and 
intermediate . 


. 


. 


* 

. 


. 

. 


-64- 


VI  o LITERATURE  CITED. 

1.  Atanasof  f , D.,  and  Johnson,  A.  G.  Treatment  of  cereal  seeds  "by 

dry  heat.  Journ.  Agric.  Research.  13:379-390.  Jan.  1920. 

2.  Branstetter,  B.  B.  Treatment  of  seed  to  control  root  and  stalk 

rots.  Ahst.  Phytopath.  12:30.  1922. 

3.  Burgess,  J.  L.  Relation  of  varying  degrees  of  heat  to  the  via- 

bility of  seeds.  Journ.  Am.  Soc.  Agron.  11:118-120.  1919. 

4.  de  Ong , E.  R.  Effect  of  excessive  sterilization  measures  on  the 

germination  of  seeds.  Journ.  Econ.  Ent.  12:343-345.  1919 

5.  Dickson,  J.  G.  Dry  heat  treatment  for  control  of  cereal  seed- 

borne  diseases.  Annual  Rpt.  Director,  1919-1920.  Wise. 
Agric.  Expt,  Sta.  Bull.  323.  Dec.  1920. 

6.  Duddleston,  B.  H.  The  modified  rag  doll  and  germinatdr  box. 

Purdue  University  Agric.  Exp.  Sta.  Bull.  236.  1920. 

7.  Ewart,  A.  J.  On  the  power  of  withstanding  desiccation  in  plants. 

Proc.  and  Trans.  Liverpool  Biological  Soc.  11:151-159. 
1897. 


8.  Goodwin,  W.  K.  Heat  for  control  of  cereal  insects.  Ohio  Agric. 

Exp.  Sta.  Bull.  354.  1922. 

9.  Groves,  J.  F.  A method  of  prophesying  the  life  duration  of  seeds 

Trans.  111.  Acad.  Sci.  8:133-136.  1915. 

10.  Groves,  J.  F.  Temperature  and  life  duration  of  seeds.  Bot,  Gaz. 

63:169-189.  1917. 

11.  Haber landt,  I.  Die  oberen  und  unteren  Temper aturgrenzen  fur  die 

Keimung  der  wichtigeren  Samereien.  Landw.  Versuchsstation , 
17:104-116.  1874. 

12.  Harrington,  George  T.,  and  Crocker,  William.  Resistance  of  seed 

to  desiccation.  Journ.  Agric.  Research  14:525-532. 

1918. 

1 1 , 

13.  Just,  L.  Wirkung  hoherer  Temperaturen  auf  die  Keimffa higkeit  der 

Samen.  Bot.  Zeit.  33:51-52.  1875. 

14.  Lehenbauer , P.  A.  Growth  of  maize  seedlings  in  relation  to  tem- 

perature. Phys.  Researches  1:  no.  5.  247-288.  1914. 

15.  Montgomery,  E.  G.  Heating  seed  rooms  to  destroy  insects.  Jourr 

Am,  Soc.  Agron.  9:105-103.  1917. 

16.  Waggoner,  H.  D,  The  viability  of  radish  seeds  (Raphanus  sativus 

L.)  as  affected  by  high  temperatures  and  water  content. 

Am.  Journ.  Bot.  4:299-313.  1917. 


-65- 


17.  Walker,  J.  C.  Seed  treatment  and  rainfall  in  relation  to  the 

control  of  cabbage  black-leg.  U.  S.  Dept.  Agric.  Bull. 
1029.  1-27.  1922. 

18.  White,  Jean.  The  ferments  and  latent  life  of  resting  seeds. 

Proc.  Royal  Soc.  London,  Series  B.  81:417-441.  1909. 


-66- 

VII.  VITA. 

Aaron  Raymond  Kienholz  was  born  October  18,  1894  near  Bellingham, 
Lac  Q,ui  Parle  County,  Minnesota. 

He  received  his  high  school  education  at  Big  Stone  City,  South 
Dakota,  graduating  in  1913.  He  attended  North-Western  College, 
Naperville,  111.  from  1913-1917  receiving  his  B.  S.  degree  in  1917. 
He  attended  the  University  of  Illinois  from  1917-1920,  receiving 
his  M.  S.  degree  in  Botany  in  June  1920.  He  attended  summer  school, 
University  of  Minnesota,  Minneapolis,  Minn.  1921, 

He  was  research  assistant  in  botany,  University  of  Illinois  1917- 
18,  assistant  in  botany  and  plant  physiology,  University  of  Illinois 
1919-1920,  1920-1921.  He  was  fellow  in  botany  1921-1922. 

He  was  Field  Assistant  in  Blister-Rust  Control,  TJ.  S.  Dept,  of 
Agriculture,  3 months  in  1917  and  5 months  in  1919,  and  was 
Assistant,  U.  S.  Forest  Service,  at  Ephriam,  Utah,  3 months  in  1920. 

He  served  8 months  in  the  U.  S.  Army  1918-1919,  5 months  of 
this  in  the  A.  E.  F.  France. 


UNIVERSITY  OF  ILLINOIS-URBANA 


12  108856466 


